It is known in the plastic field to incorporate fillers into resins to provide various advantages known in the art. When light coloured plastics are to be prepared, the fillers of choice are calcium carbonate (also known as calcite), silica, dolomite and talc. The essential characteristics of the common filler are shown in Table I.
TABLE I ______________________________________ COMMON INORGANIC FILLERS Density Filler Formula lb/ft.sup.3 Whiteness ______________________________________ Calcite CaCO.sub.3 55 80 Dolomite CaCO.sub.3.MgO 65 55 Silica SiO.sub.2 40 85 Talc 3MgO.4SiO.sub.2.H.sub.2 O 45 75 ______________________________________
Since the naturally occurring inorganic fillers are mined products mining costs becomes an important factor in their price. Also they present a disadvantage when they are to be used as fillers in lightweight plastic materials since in these cases a filler having a density lower than 40 lb/ft.sup.3 will be required.
On the other hand, asbestos tailings as such could not be used as filler because of the presence of short asbestos fiber and because they have a bulk density of from about 40 to about 60 lb/ft.sup.3 and in some cases their degree of whiteness is too low.
Accordingly, it would be highly desirable if means could be found to modify asbestos tailings by substantially reducing their specific gravity so that they could be used as lightweight fillers in plastics while maintaining their degree of whiteness within an acceptable level when compared with common in organic fillers such as dolomite and talc.